1. Field of Invention
The present invention relates to a jack, and more particularly to a hydraulic jack with dual pump system, which can quickly lift up a drive piston to raise a load while being energy effective.
2. Description of Related Arts
A conventional hydraulic jack comprises a lifting arm movably disposed in a base, a handle mounted on the base, and a hydraulic system which comprises a fluid cylinder for receiving a hydraulic fluid and a piston connected to the lifting arm in such a manner that when the handle is pulled and pushed repeatedly to pump the hydraulic fluid to drive the piston upwardly, the lifting arm is lifted upwardly for raising a load thereon.
Accordingly, the handle is repeatedly operated in a no load condition or in a light load condition to raise the lifting arm by the piston in a very slow speed. For example, when the lifting arm is lifted up approximately 50 to 60 centimeters from an original storage position to an initial lift up position, the handle must be required to pull and push about twenty times. In other words, even though there is no load on the lifting arm, the lifting operation requires the same speed as normal. Therefore, the lifting operation is time and labor consuming such that the load cannot be immediately raised, especially in an emergency situation, by the lifting arm in response to the handle.
An improved hydraulic jack is capable of speeding up the lifting operating in the no load condition. For example, U.S. Pat. No. 5,755,099, owned by Hung, generally suggests a hydraulic jack comprising a hydraulic cylinder having a hollow piston rod to form an inner oil chamber wherein an oil guide tube is slidably inserted into the piston rod to guide the hydraulic fluid flowing into the inner oil chamber. The second oil channel is extending between the pump oil chamber and the inner oil chamber of the piston wherein the second check valve is located in the second oil channel to allow hydraulic flow from the pump oil chamber into the inner oil chamber of the piston rod when the plunger is moved into the pump oil chamber. The third check valve is located in the third oil channel to allow hydraulic flow from the outer reservoir into the inner chamber and to prevent flow in the opposite direction. The fourth oil channel is extending between the inner chamber and the second oil channel ahead of the second check valve. The sequence valve is opening at the predetermined control pressure to enable hydraulic flow from the second oil channel into the inner chamber.
When operating the hydraulic jack, the hydraulic fluid is not only pumped into an inner chamber of the hydraulic cylinder to push the piston rod at the back thereof forwardly but also filled into the inner oil chamber to apply an additional pushing force against the piston rod. Therefore, in the no load condition, the lifting arm is capable of being lifted up quickly. However, such hydraulic jack has several drawbacks.
Since the hollow shaped piston rod is constructed to have the inner oil chamber therein, the stiffness structure of the piston rod will be substantially weakened. The main purpose of the piston rod is to pull the lifting arm upwardly so as to lift up the load having at least hundreds lbs. Due to the safety reason, it is unreasonable for a use to use the weak but quick loading hydraulic jack because any mistake may cause an unwanted injury to the user, especially in an emergency situation. Furthermore, an O-shaped sealing ring must be mounted on the oil guide tube to provide an air sealed condition between the oil guide tube and the piston rod so as to prevent the hydraulic fluid from leaking at the inner oil channel. However, the sealing ring will be torn out after a period of time. Once the sealing ring is broken, the hydraulic fluid will be leaked from the inner oil chamber. In other words, the hydraulic jack cannot provide the quick lifting feature and is dangerous for the user.
Moreover, the structural design of the piston rod can provide a quick lifting operation of the lifting arm. It means that the lifting arm will be dropped down quickly when the hydraulic fluid is returned back to the container since the hydraulic fluid is quickly flow back to the container from the inner oil chamber of the piston rod. In addition, if one of the check valves is broken, the entire hydraulic jack cannot be operated. It is unsafe that when the user accidentally releases the hydraulic fluid from the hydraulic cylinder. Due to the gravity, the downward force of the weight of the load will accelerate the downward movement of the lifting arm. It is dangerous when the user cannot respond immediately to stop the dropping down of the load.
A main object of the present invention is to provide a hydraulic jack with dual pump system, which can quickly lift up a drive piston to raise a load while being energy effective.
Another object of the present invention is to provide a hydraulic jack with dual pump system which can double up the hydraulic fluid flowing to push the pusher piston forward so as to speed up the lifting operation of the hydraulic jack in no load or light load condition.
Another object of the present invention is to provide a hydraulic jack with dual pump system, wherein the pusher piston is constructed to have a solid member so as to enhance the stiffness of the pusher piston.
Another object of the present invention is to provide a hydraulic jack with dual pump system, wherein the dual pump system allows the hydraulic fluid flowing back to the hydraulic fluid tank slowly, so that the lifting arm of the hydraulic jack is slowly dropped down while the unloading operation, so as to prevent the lifting arm suddenly dropping drown to cause an injury of the user.
Another object of the present invention is to provide a hydraulic jack with dual pump system, wherein the hydraulic cylinder is constructed to be encircled by the first fluid reservoir where the hydraulic fluid is stored therein, so as to substantially not only protect the hydraulic cylinder by the first fluid reservoir but only reduce a size of the hydraulic jack in comparison with the conventional hydraulic jack that the hydraulic fluid tank is mounted at a position behind the piston shank.
Accordingly, in order to accomplish the above objects, the present invention provides a hydraulic jack, comprising:
a base frame;
a lifting arm having a pivot end pivotally mounted on the base frame and a lifting end arranged in such a manner that when the pivot end of the lifting arm is moved forwardly, the lifting end of the lifting arm is driven to move upwardly;
a hydraulic cylinder, having an inner fluid chamber, mounted on the base frame;
a piston shank having a driving portion movably disposed in the fluid chamber and a pusher head solidly extended from the driving portion towards the lifting arm to push the pivot end of the lifting arm forward;
a first fluid pump system comprising a first fluid reservoir for storing a hydraulic fluid therein and a first fluid circuit comprising a first fluid passing channel extending between the first fluid reservoir and the inner fluid chamber of the hydraulic cylinder, a first pumping means for pumping the hydraulic fluid from the first fluid reservoir to the inner fluid chamber, a first check valve located at the first fluid passing channel for preventing a flow of hydraulic fluid in a reverse direction, a first fluid returning channel extending between the first fluid reservoir to the inner fluid chamber, and a first sequence valve located at the first fluid returning channel and opening at a predetermined control pressure to enable the hydraulic fluid flowing from the inner fluid chamber back to the first fluid reservoir;
a second fluid pump system comprising a second fluid reservoir communicatively connected with the first fluid reservoir and a second fluid circuit comprising a second fluid passing channel extending between the second fluid reservoir and the inner fluid chamber of the hydraulic cylinder, a second pumping means for pumping the hydraulic fluid from the second fluid reservoir to the inner fluid chamber, a second check valve located at the second fluid passing channel for preventing a flow of hydraulic fluid in a reverse direction, a second fluid returning channel extending between the second fluid reservoir to the inner fluid chamber, and a second sequence valve located at the second fluid returning channel and opening at a predetermined control pressure to enable the hydraulic fluid flowing from the inner fluid chamber back to the second fluid reservoir, wherein the control pressure preset at the first sequence valve is smaller than that preset at the second sequence valve; and
an actuation handle pivotally connected to the base frame and arranged to drive the lifting arm from a no load condition to a load condition, wherein at the no load condition, both the first and second pumping means are respectively pumping the hydraulic fluid from the first and second fluid reservoirs to the inner fluid chamber of the hydraulic cylinder to push the driving portion of the piston shank forward, so as to speed up the lifting up of the lifting arm, and at the load condition, the first sequence valve is opened for allowing the hydraulic fluid flowing back from the inner fluid chamber to the first fluid reservoir by means of a loading pressure, while the second pumping means keeps pumping the hydraulic fluid to the inner fluid chamber to substantially lift up the lifting arm.